Time delayed actuators are widely employed to switch relay contacts, open and close fluid control valves, and operate many other types of mechanisms. Electrical and electronic timers are perhaps the most commonly used devices of this type. In certain applications, however, such timers are impractical because of their expense, complexity and/or need for a power supply.
As an alternative to the electrical timer, a dashpot type of delayed actuator may be utilized. This mechanism includes a piston disposed within a fluid-filled cylinder. As the piston is moved through the cylinder, fluid is forced through a circumferential gap between the piston and the cylinder wall so that the piston gradually changes from a first state to a second state.
A rotary plate delayed actuator is used to slow the motion of cassette tape machine doors and record player armatures. This device employs a pair of parallel plates that are separated by a layer of viscous fluid. Torque is applied to one of the plates while the other is held fixed, and the viscous drag of the fluid slows the motion of the movable plate.
Typically, dashpot and rotary plate devices are effective for providing delays of only a few seconds. In order to extend their delay periods, their fluid reservoirs must be made impractically large. Increasing the delay of the dashpot device requires making the circumferential gap exceedingly and impractically small. Moreover, both devices must be hermetically sealed to prevent escape or contamination of the fluid, and each requires at least one precision tolerance (i.e., the dashpot piston/cylinder clearance and the rotary plate spacing) which adds significantly to the cost of the device.
There is a particular need for an inexpensive, easy to manufacture, and effective time delayed actuator system for the dispensing of fragrances, insecticides, and other airborne fluids. Present dispensers are typically either passive or active. Passive devices employ a container filled with a fluid. A wick protruding from the fluid-filled container absorbs the fluid and emits it into the air. These systems do not employ extremely volatile fluids because such fluids evaporate too rapidly. As a result, the dispensing rate of these devices is often not sufficient to perform the function desired, e.g., the elimination of offensive odors.
Less volatile fluids may be dispensed more effectively with an active device that employs an electric blower or heater to stimulate emission. However, such devices are fairly expensive and again require a source of electrical power.
Prior art devices, such as Carter et al. U.S. Pat. No. 4,742,189 and U.S. Pat. No. 4,791,251, disclose visco-elastic delayed actuators which have adequately long timing periods of minutes to hours. However, they are difficult to manufacture because the adhesive itself must be applied directly to the engaging surfaces in such a way as to precisely control layer thickness and final consistency. This generally requires an above boiling temperature pressurized delivery system with a particular temperature gradient in the delivery lines and, additionally, a specially designed nozzle. This requirement makes final assembly of prior art devices messy and time consuming. It additionally requires that a new delivery system be designed, constructed, and debugged each time a new device geometry is contemplated.